flow rate for C25 on sheet metal with Mig

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Hello all, i have been browsing the boards for some time but have not registered until now.  i live in Md. and purchased a Miller 140 Autoset this past year for some resto work on my '70 Porsche 911.  i did take a welding class before purchasing the machine and was exposed to everything from stick (love seeing slag peel off 6013 welds!) to Mig to Tig.  our instructor was a sharp guy and we got a LOT of hands on experience.  i currently have my regulator set at 25cfh for C25 and things are going okay but after reading a post here that mentioned 15cfh i thought i'd ask if 25 was acceptable.  i am replacing the suspension pan in my car and doing a lot of plug welds on 22-18ga metal.  i recently learned that switching to lower power and a very short stickout makes a world of difference in thin metal.  my welds have improved greatly and i am reasonably happy with my work now.one other question i have is regarding self tapping screws.  there are certain areas that i simply can not get a clamp on and it seems i need to use screws.  is there a type, size or brand i should be looking for?  i was hoping to pick some up at Home Depot if possible.  Thanks for the input!Erik
Reply:The shielding gas is for shielding the atmosphere away from the molton puddle and in some shops, where there is no fan or open windows open, 15 might be ok but 25 is ok also.  If you get to much gas flow, it will cause porisity.  Have fun and welcome.  John   SMAW,GMAW,FCAW,GTAW,SAW,PAC/PAW/OFCand Shielding Gases.  There all here. :
Reply:Ballpark number for shield gas flow rate for manual MIG welding (GMAW) is usually 20 cfh, give or take.  Generally +/- 5 cfh is in the usually OK range.  YMMV, depending on wind or breeze conditions and also the torch size and stick-out distance.  Bigger torch and bigger wire diameter and bigger amp settings and bigger stick-out/stand-off distance may call for a little more gas flow.The purpose of the shielding gas is to shield the weld from the atmosphere.  To low of a flow rate and it might not shield the arc.  To high of a flow rate and the air can actually get sucked into the welding zone (via flow turbulence).You want to 'blanket' the weld with the shielding gas, not blow a forceful stream of gas around.note: TIG (GTAW) uses gas to not only shield the weld during welding, but also to cool and protect the hot tungsten electrode while it cools off after you stop the arc.  That's the "post flow timer" setting.  Hot tungsten exposed to atmosphere becomes an oxidized tungsten, so that means you have to grind off the crud from the electrode before trying to continue welding.To test for the effects of flow rates on your typical set-up, do some experimenting with 'typical' conditions and set-ups for you.  If you usually weld overhead on sheet metal with a fan blowing cross-wise for ventilation, then do some practice in such a set-up with different flow rates.  Back down on the flow until the weld starts to go bad (assuming you can do OK welds to start with).  That is then too low of a flow rate.  Use a little more than that flow rate and you should be good.  Turn up the flow rate and see if you start to get bad welds again because of air entrainment when the flow is too high.  That flow rate is too high.Higher than needed flow rates just waste gas (as long as you haven't gotten to the air entrainment/turbulent flow problem area, which wastes gas AND makes bad welds).
Reply:thanks guys, i will dial back to 20 and see how she goes.
Reply:On another thread I put 1.25 cf/hour when I meant 12.5 cf/hr. This is what I have mine set at and get excellent results. Now keep in mind that this is done indoors and even the tiniest breeze can affect it adversely. If the breeze is bothering me I turn up a small amount. If that doesn't fix the problem I set up wind screens. The less you use the less it costs you.The difference between art and craft is the quality of the workmanship. I am an artist.